JPH10270801A - Nitride III-V compound semiconductor light emitting device and method of manufacturing the same - Google Patents

Abstract

(57) [PROBLEMS] To provide a nitride-based III-V compound semiconductor device having a flat resonator surface or stripe structure without using cleavage or etching. SOLUTION: In a nitride-based III-V compound semiconductor device, two parallel surfaces of a hexagonal prism structure formed by selective growth on a substrate are used as resonator surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a nitride III-
More particularly, the present invention relates to a nitride-based III-V compound semiconductor light emitting device using a hexagonal column structure and a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, a method using the cleavage of a substrate is used for manufacturing a resonator surface of a laser. However, usually, the sapphire substrate used for the nitride-based III-V compound semiconductor light emitting device has no cleavage,
As described in JP-A-8-17803,
Nitride II laminated on sapphire substrate as insulator
The resonator is formed by dry-etching the group IV compound semiconductor light emitting device to the lower contact layer.

A nitride-based compound semiconductor light-emitting device manufactured using a spinel substrate (MgAl ₂ O ₄ ) is known as “I
nGaN multi-quantum-Wells
structure laser diodes gro
wn MgAl ₂ O ₄ Substrates ”, SN
akamura et al. , Appl. Phys.
Lett. 68 (1996) pp 2105-2107. FIG. 13 is a sectional view of a conventional III-V compound semiconductor light emitting device. 1 is a substrate, 2 is a first
Conductive type GaN single crystal thin film, 3 is SiO ₂ film, 4 is first conductive type Al _0.2 Ga _0.8 N clad layer, 5 is undoped I
n _0.15 Ga _0.85 N active layer, 6 is the second conductivity type Al _0.2 Ga
_0.8 N clad layer, 7 is a p-type GaN contact layer, 8 is a first conductive side electrode, and 9 is a second conductive side electrode. This II
In a group IV compound semiconductor light emitting device, a nitride III-V
A resonator is formed by polishing a group III compound semiconductor. Or "High-quality G
aN epitaxiallayer grown b
y metalorganic vapor phas
e epitaxy on (111) MgAl ₂ O ₄
Substrate ", A. kuramata et.
al. , Appl. Phys. Lett. 67 (19
95) As described in pp 2521 to 2523, a resonator is formed using the cleavage of a spinel substrate (MgAl ₂ O ₄ ).

[0004]

The use of a cleaving spinel substrate makes it easy to form a resonator surface. However, a sapphire substrate or a spinel substrate is insulative.
Even if a resonator is formed using the cleavage of the substrate, it is necessary to dry etch the upper stripe electrode side to form the lower electrode.
However, the side surface of the stripe formed by the etching is not flat, which has a large effect on light loss during laser oscillation, and causes a problem that the threshold current of laser oscillation is increased.

The present invention has found a method of forming the cavity end face and the stripe side face which solves the above-mentioned problems,
The purpose is to reduce the threshold current of laser oscillation.

[0006]

SUMMARY OF THE INVENTION The nitride III of the present invention
A -V compound semiconductor light emitting device is a nitride III-V formed by stacking nitride III-V compound semiconductors.
In the group III compound semiconductor light emitting device, the nitride III
The -V group compound semiconductor has a hexagonal column shape, and two planes parallel to the hexagonal column are used as resonator surfaces.

[0007] The present invention is characterized in that one pair of opposing areas of the resonator surface is 0.2 or less in opposing areas of the other two pairs.

Further, the method for manufacturing a nitride-based III-V compound semiconductor light-emitting device comprises the steps of:
Growing a group-V compound semiconductor; forming an oxide film on the first nitride-based III-V compound semiconductor; and forming the oxide film until the first nitride-based compound semiconductor is exposed. Forming a window by partially etching the film; and forming a second nitride-based II having a hexagonal prism structure from the window.
The method is characterized by growing an IV group compound semiconductor.

The window has a hexagonal shape, and when one set of parallel facing lengths is 1, the other two facing lengths are 0.2 or less.

[0010] Further, the shape of the window is rectangular, and the ratio of the length of the long side to the short side is 22 / (7 × (3) ^0.5 ) or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a sectional view showing a manufacturing process for manufacturing a hexagonal prism laser. Although not shown, a first conductivity type G is provided on the substrate 1 through a low-temperature grown GaN buffer layer.
An aN single crystal thin film 2 is grown by MOCVD. FIG. 1A is a perspective view of the manufacturing process at this time.

Next, a SiO ₂ film 3 is deposited on the first conductivity type GaN single crystal thin film 2 by a CVD method, a resist is applied thereon, and a hexagonal window is formed by photolithography. Next, the SiO ₂ film 3 is partially removed to the first conductivity type GaN single crystal thin film 2 by dry etching using the resist as a mask, and the resist is further removed. FIG. 1B is a perspective view of the manufacturing process at this time.

Next, the substrate 1 is introduced again into the MOCVD apparatus, selective growth is performed using the SiO ₂ film 3 as a mask, and a first conductivity type AlGaN cladding layer 4 is sequentially grown on the window portion.

Further, an undoped InGaN active layer 5, a second conductivity type AlGaN cladding layer 6, and a second conductivity type GaN contact layer 7 are successively grown. Finally, the SiO
_{The two} films 3 are removed, the first conductive side electrode 8 and the second conductive side electrode 9 are formed by photolithography, and a laser can be manufactured by dividing the chip. FIG. 1D is a perspective view of the manufacturing process at this time.

By selecting the crystal growth conditions of the nitride III-V compound semiconductor, it becomes possible to grow the crystal only in the window portion. In this case, the MOCVD method was the more superior crystal growth method.

In the hexagonal column grown in the window portion, it is more preferable that the crystal is gradually enlarged from one crystal nucleus from the initial stage of growth. However, even when a plurality of hexagonal prisms are generated in the initial stage of growth, each hexagonal prism can be combined into one hexagonal prism by optimizing the crystal growth rate. The growth of the hexagonal prism in the in-plane direction stops when the pattern of the window is reached, and thereafter growth proceeds only in a direction perpendicular to the plane.

In the present embodiment, a nitride-based III-V compound semiconductor light emitting device selectively grown from three different hexagonal windows was manufactured. FIG. 2 shows the shape of the window at this time. The shape of the window shown in FIG. 2A is a regular hexagon, and one side a is 30 μm.

The window pattern shown in FIG. 2B has a shape in which one set of parallel opposing lengths is set to 1 and the other two sets of opposing lengths are set to 0.2. It was square, with the short side a being 30 μm and the long side being 65 μm. Here, the opposing length is the length of the short side of the largest rectangle formed by drawing a perpendicular to the parallel side.

The window pattern shape shown in FIG. 2C is such that when one set of parallel facing lengths is set to one, the other two
The pair has a shape in which the opposing length is 0, and the short side a is 30 μm.
m, and the long side was 90 μm.

The layer structure of the laser formed from such a window has an n-type GaN layer (thickness 0.2 μm, carrier concentration 1 ×).
10 ¹⁹ cm ⁻³ ), n-type Al _0.2 Ga _0.8 N clad layer (1.0 μm in thickness, 5 × 10 ¹⁷ cm ⁻³ carrier concentration), i-type In _0.15 Ga _0.85 N active layer (60 μm in thickness), p Type Al
_{It comprises a 0.2} Ga _0.8 N cladding layer (film thickness 0.8 μm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) and a p-type GaN contact layer (film thickness 0.2 μm, carrier concentration 5 × 10 ¹⁸ cm ⁻³ ). . The drive current was a pulse current having a pulse width of 1 μsec and a pulse period of 1 msec.

FIG. 3 shows an oscillation spectrum of the structure of the nitride III-V compound semiconductor light emitting device of the present invention grown from the window shown in FIG. 2C. As shown in FIG.
The oscillation spectrum of the laser has a substantially single peak, and the uniformity of the oscillation wavelength is improved as compared with a conventional laser having an electrode stripe structure. This is because, when a hexagonal prism structure is used as in the present invention, the cavity length of the laser is determined only by the size of the hexagonal prism structure. This is because the oscillation laser of the above can be realized.

On the other hand, in the case of forming the end face of the resonator by cleavage in the related art, several hundred μm
Because of the above limitations, single-wavelength oscillation is difficult. If the size of the hexagonal column is too small, it becomes difficult to form the upper electrode. Therefore, the length of the resonator is preferably 10 μm or more.

FIG. 4 shows the relationship between the injected current density and the light output of a nitride III-V compound semiconductor light emitting device manufactured by growing from different hexagonal windows. As compared with a conventional laser manufactured using polishing and dry etching with the same layer structure as in this embodiment, FIG.
In the structures grown from the windows shown in (b) and (c), the threshold current density could be reduced. This is because when the two parallel surfaces of the hexagonal prism structure of the present invention are used as the resonator surface, the surface of the hexagonal prism structure is a flat surface in the atomic order, so that the resonator formed by polishing or the like is used. This is because the flatness is significantly improved as compared with the surface or the ridge side surface formed by dry etching, and as a result, light loss on the resonator surface and the ridge side surface is significantly reduced. On the other hand, in the case of FIG. 2A, since the resonator surface was formed in three directions, the light confinement efficiency was poor, and no oscillation occurred.

As shown in FIG. 4, the threshold current density decreases as the facing area of one side becomes larger than the facing area of the other side. This is because, when the hexagonal prism structure is a regular hexagon, laser oscillation occurs in three resonator plane directions, which causes an increase in threshold current density. FIG. 5A shows a schematic diagram of the oscillation in this state. In order to reduce the threshold current density, it is necessary to make the facing area of one set of parallel faces of the hexagonal prism larger than the facing areas of the other two sets of faces. Assuming that the length of one set of long sides is b and the other longest side is a, a nitride III-V compound semiconductor light emitting device grown from a hexagonal window satisfying b ≧ 15a / 7 A schematic diagram of the oscillation is shown in FIG. The shape of the window is a hexagon, which is a shape in which one pair of parallel opposing lengths is 1 and the other two pairs of opposing lengths are 0.2,
It is shown that laser oscillation occurs from almost one direction and laser oscillation occurs from the other two directions slightly.

When a hexagonal window that satisfies b ≧ 3a is used, a resonator is formed only in one direction and no resonator is formed in the other two directions. Become. A schematic diagram of the oscillation in this case is shown in FIG.

The opposed length of a set of parallel long side surfaces is b
And c is the facing length of the other two sets of parallel surfaces,
Taking c / b in the hexagon of the window pattern shape as the horizontal axis, c
FIG. 6 shows the correlation between the threshold current density at / b and the threshold current density at c / b = 0 on the vertical axis. Practically, the threshold current density at the time of c / b = 0 is preferably up to twice.

Ideally, the resonator is formed only in one direction, that is, when the hexagon of the window pattern shape is c / b = 0, that is, when b ≧ 3a,
As shown in FIG. 6, in practice, the threshold current is greatly reduced as compared with the laser of the conventional structure by making the opposing length of the other two sets less than 0.2 with respect to the opposing length of one set. It is possible and considered practical. In this case, the condition that the hexagon of the window pattern shape is b / a = 15/7 or less should be satisfied.

(Embodiment 2) In Embodiment 1, it is possible to obtain a hexagonal prism structure by providing a window having the same shape as the hexagonal prism structure of the laser to be formed. In this embodiment, an oxide film having three different rectangular windows is used as a mask for selective growth. FIG. 7 is a top view of a semiconductor laser having a hexagonal column structure grown from a layer made of a rectangular window.

The length of the short side of the rectangular window is 50 μm, and the window shown in FIG. 7A is a rectangle (long side length 57.5 μm) in which the ratio of the long side to the short side is 1.15. Yes, Figure 7
The window shown in (b) has a long side to short side ratio of 2.0 (ratio of 22
The window shown in FIG. 7C has a rectangular shape (long side of 100 μm) having a length of not less than / (7 × (3) ^0.5 ) and not more than 4 / (3) ^0.5 . (Ratio of 4 / (3) ^0.5 or more) is a rectangle (long side length 125 μm). A nitride III-V compound semiconductor light emitting device was manufactured in the rectangular shape of the window by using the same manufacturing process as in the first embodiment.

FIG. 7 shows a regular hexagonal laser having a hexagonal prism structure.
FIG. 7B shows a hexagonal column laser in which one set of parallel facing lengths shown in (a) is 1 and the other two sets of facing lengths are 0.2 or less. FIG. 7C shows a hexagonal column in which one set of parallel opposing lengths is set to 1 and the other two sets of opposing lengths are set to 0.

FIG. 8 shows current-light output characteristics of lasers grown from different rectangular windows. The layer structure of the laser is the same as that of the first embodiment. The driving current is a pulse current having a pulse width of 1 μsec and a pulse period of 1 msec. As is clear from FIG. 8, the threshold current density decreases as the longer side of the rectangle becomes larger than the shorter side. In the regular hexagonal structure shown in FIG. 7A, oscillation did not occur.

In order to obtain an ideal hexagonal prism structure as shown in FIG. 7C, the ratio of the long side to the short side of the rectangle is set to 4 /
(3) It must be ^0.5 or more.

Ideally, a resonator is formed only in one direction, but in an actual laser, if one set of opposing areas is set to 1, the other two sets of opposing areas are set to 0.1. Even if it is about 2 or less, as described in the first embodiment, it is possible to greatly reduce the threshold current as compared with the laser having the conventional structure. The ratio may be set to 22 / (7 × (3) ^0.5 ) or more.

(Embodiment 3) A set of parallel sides in a hexagonal or rectangular window pattern shape and six equivalent a-axes of a nitride III-V compound semiconductor that is hexagonal Desirably, it is perpendicular to one. FIG. 9 shows the relationship between the crystal plane of the nitride-based compound semiconductor and the a-axis.
As shown in FIG. 9, this is because the wall surface of the hexagonal prism structure is a surface orthogonal to the a-axis. In the case of actual crystal growth, the conditions can be relaxed a little, and 90 ° ± 5 °
It is sufficient if it is within the angle range.

When SiC is used as the substrate, FIG. 10A shows the shape of a window formed such that the long side of the rectangle forms an angle of 90 ° with respect to the a-axis of the SiC substrate. Next, FIG. 10B shows the shape of a window formed such that the long side of the rectangle forms an angle of 45 ° with respect to the a-axis of the nitride III-V compound semiconductor. Further, FIG. 10C shows the shape of a window formed such that the long side of the rectangle forms an angle of 60 ° with respect to the a-axis of the nitride III-V compound semiconductor. FIG.
In the window shapes shown in FIGS.
The figure also shows a hexagonal prism structure formed by growing a group V compound semiconductor. The rectangular shape was a rectangle (long side length 125 μm) with a ratio of long side to short side of 2.5, and was the same. According to this figure, the most desirable nitride having a hexagonal prism structure is a window pattern shape in which the long side of the rectangle is formed at an angle of 90 ° with respect to the a-axis on the SiC substrate shown in FIG. It can be seen that a group III-V compound semiconductor is formed.

In general, the crystal growth direction of a compound semiconductor is
It is determined by the crystal structure and the plane orientation of the substrate 1. Substrate 1
When a (001) plane (c-plane) of a material having a wurtzite structure such as 6H—SiC is used as an example, the a-axis of the substrate and the a-axis of GaN, which is a nitride III-V compound semiconductor, are completely The window may be formed so as to be coincident and the long side of the rectangle to be orthogonal to this. When sapphire is used as the substrate, the a-axis of GaN is 30 ° relative to the a-axis of sapphire.
Since GaN grows in the rotated direction, a window may be formed so that the long side of the rectangle is rotated by 30 ° of the sapphire substrate.

FIG. 11 shows current-light output characteristics of a laser manufactured using the same manufacturing process as that of the first embodiment. The layer structure of the laser is the same as that of the first embodiment. The driving current has a pulse width of 1 μsec and a pulse period of 1 msec.
Pulse.

As is clear from FIG. 11, FIG.
The resonator surface of the nitride-based III-V compound semiconductor light emitting device shown in FIG.
In the nitride III-V compound semiconductors shown in (b) and (c), the oscillation efficiency was very poor. FIG.
In the cases of (b) and (c), the obtained nitride III-
The shape of the group V compound semiconductor was not constant. Therefore, it is preferable that a set of parallel sides of a hexagon or a rectangle is perpendicular to one of three equivalent a-axes of a nitride III-V compound semiconductor having a hexagonal system.

In the embodiment, the hexagonal prism structure having two orthogonally symmetric axes shown in FIG. 12A is described, but one hexagonal prism structure as shown in FIG. FIG. 12 shows a hexagonal prism structure having a symmetric axis, and FIG.
Laser oscillation is possible even with a hexagonal prism structure as shown in FIG. 3C. However, when the facing area of one set of the resonator surfaces is 1, the facing area of the other two sets is 0.2 or less. It is preferred that it is.

The present invention relates to a nitride III-
GaN, InGaN, Al
The present invention can be applied to other than GaN, for example, BN.

[0041]

The use of the laser structure found in the present invention facilitates fabrication of a resonator and a laser device, improves the characteristics of a nitride-based III-V compound semiconductor device, and further facilitates simpler fabrication. A one-wavelength oscillation laser can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a manufacturing process of a laser device having a hexagonal prism structure according to the present invention.

FIG. 2 is a view showing a shape of a window according to the present invention.

FIG. 3 is a diagram showing an oscillation spectrum of the laser according to the first embodiment.

FIG. 4 is a diagram showing current-light output characteristics of the laser according to the first embodiment.

FIG. 5 is a diagram showing the relationship between the resonator surfaces of the laser having the hexagonal prism structure shown in the first embodiment.

FIG. 6 is a diagram showing a correlation between c / b and the ratio of the threshold current density to the threshold current density when c / b = 0.

FIG. 7 is a top view of a hexagonal column structure laser grown from a rectangular window according to the second embodiment.

FIG. 8 is a diagram showing current-light output characteristics of the laser according to the second embodiment.

FIG. 9 is a diagram showing a relationship between an a-axis and a crystal plane of a nitride-based compound semiconductor crystal.

FIG. 10 is a top view of a hexagonal column structure laser grown from a rectangular window according to the third embodiment.

FIG. 11 is a diagram showing current-light output characteristics of the laser according to the third embodiment.

FIG. 12 illustrates lasers with various hexagonal prism structures.

FIG. 13 is a diagram showing a laser having a conventional structure.

[Explanation of symbols]

Reference Signs List 1 substrate 2 first conductivity type GaN single crystal thin film 3 SiO ₂ film 4 first conductivity type AlGaN cladding layer 5 undoped InGaN active layer 6 second conductivity type AlGaN cladding layer 7 second conductivity type GaN contact layer 8 first conductivity side electrode 9 Second conductive side electrode

Claims (5)

[Claims] 1. A nitride III-V compound semiconductor light emitting device formed by laminating nitride III-V compound semiconductors, wherein the nitride III-V compound semiconductor has a hexagonal column shape, A nitride III-V compound semiconductor light-emitting device having two parallel planes of the hexagonal prism as resonator surfaces. 2. The nitride III-type according to claim 1, wherein the other two sets of opposing areas of the resonator surface are set to 0.2 or less with respect to one set of opposing areas. Group V compound semiconductor light emitting device. 3. a step of growing a first nitride III-V compound semiconductor on a substrate; a step of forming an oxide film on the first nitride III-V compound semiconductor; Forming a window by partially etching the oxide film until the first nitride-based compound semiconductor is exposed; and forming a second nitride-based III-V compound semiconductor having a hexagonal column structure from the window. Growing nitride-based II
A method for manufacturing an IV compound semiconductor light emitting device. 4. The shape of the window is hexagonal, and when one pair of parallel opposing lengths is 1, the other two pairs of opposing lengths are 0.2 or less. The method for manufacturing a nitride-based III-V compound semiconductor light-emitting device according to claim 3. 5. The nitride according to claim 3, wherein the shape of the window is a rectangle, and the length of the long side to the short side is a ratio of 22 / (7 × (3) ^0.5 ) or more. System III
-A method for manufacturing a group V compound semiconductor light emitting device.